Annals of biomedical engineering
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Comparative Study
Intrathoracic pressure fluctuations move blood during CPR: comparison of hemodynamic data with predictions from a mathematical model.
Whether blood flow during cardiopulmonary resuscitation (CPR) results from intrathoracic pressure fluctuations or direct cardiac compression remains controversial. We developed a mathematical model that predicts that blood flow due to intrathoracic pressure fluctuations should be insensitive to compression rate over a wide range but dependent on the applied force and compression duration. If direct compression of the heart plays a major role, however, the model predicts that flow should be dependent on compression rate and force, but above a threshold, insensitive to compression duration. ⋯ At nearly constant peak sternal force (378-426 N), flow was significantly increased when the duration of compression was increased from short (13%-19% of the cycle) to long (40%-47%), at a rate of 60/min. Flow was unchanged, however, for an increase in rate from 60 to 150/min at constant compression duration. In addition, myocardial and cerebral flow correlated with their respective perfusion pressures.(ABSTRACT TRUNCATED AT 400 WORDS)
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Left ventricular (LV) diastolic filling is limited by the constraining effects exerted by the pericardium (PE) and the lung/chest wall. The aim of the present study was to assess the validity of various estimates of external cardiac constraint, compared to pericardial surface pressure (Ppe) measured lateral to the LV myocardium. In nine anesthetized dogs we measured Ppe, pleural surface pressure (Ppt) (lateral to the pericardium) and esophageal pressure (Pes) under conditions of volume loading and positive end-expiratory pressure (PEEP). ⋯ Therefore, calculation of transmural LV pressure by subtracting pleural or esophageal pressure from intracavitary pressure can lead to overestimation of LV preload. The decrease in cardiac output during PEEP occurs secondary to decreased preload, i.e. decreased transmural pressure and end-diastolic dimension. Analysis of performance using cardiac function curves does not suggest a change in contractility with PEEP.